Document Type : Research Paper
Authors
Monitoring and Improvement of Soil and Water Research Department, Soil and Water Research Institute (SWRI), Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran
Abstract
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EXTENDED ABSTRACT
One of the most important limitations of farming in the Sistan plain is soil salinity, which, according to the existing records in the region, is considered a very important and influential issue on the production of regional products and water management. Due to low rainfall, limited water resources, increasing temperature, decreasing relative humidity and increasing evaporation, the agricultural lands of Sistan plain show various degrees of salinity and alkalinity. Therefore, the quantitative determination of spatial and temporal changes can be important as decision-making components in irrigation management and exploitation of agricultural inputs and products. Also, knowing the state of soil salinity distribution of this plain plays an important role in choosing lands with less restrictions for project implementation and optimal management of water and soil resources. For this reason, knowledge of the soil salinity will help in the proper management of crop production.
To study the salinity situation using remote sensing for different sites in Sistan Plain, Landsat (LC08-LOI/TIRS) satellite images were used in April, August and November of 2017 and April of 2018. The initial correction processing was related to change voltage to digital number (DN) via converting radiance data was done by satellite calibration file and data radiometric correction using flat field method in ENVI 5.1 software. To determine the soil sampling points, using a 2x2 km grid and by referring to the area and checking the sampling location, 312 soil samples were taken. Then the values of soil Electrical Conductivity (EC), Sodium Absorption Ratio (SAR) and texture were measured. Using cross-validation, 75% of the samples were considered as training data and 25% of them considered for the testing data. The spectral characteristics of the satellite images were extracted via secondary correction processing. Salinity map was prepared for the surface soils of the region in four periods using several algorithms and indices.
The results of the remote sensing investigation showed that surface soil salinity in the region is a dynamic phenomenon and has significant changes with the changes of season, rainfall, irrigation and land management. For example, in the northeast of Zahak 3, in the summer, more lands have high salinity, but at the end of winter and the beginning of April, the percentage of lands with high salinity has decreased in that region. The results showed that in August 2017, the surface of the land with EC more than 8 dS/m were more than the other seasons. On the other hand, the land surface with salinity less than 4 dS/m had the highest value in April 2018, which could be due to the increase in rainfall and flooding in the region at this time. After that, in November 1997, the largest area of land with salinity less than 4 dS/m was observed. The results obtained from the interpretation of satellite images showed parameters such as time, rainfall events of the planting season and water and soil management have a significant effect on soil salinity and the areas of lands with different salinity. The extent of soils with high salinity increased in the summer season, but in April 2018 (which coincided with the sampling), this extent decreased, due to the occurrence of rains and floods in these areas.
Salinity changes can be considered in general scale and farm scale. On a general scale, the location of the lands in relation to the Pozak Saburi and Hirmand mountains and the course of the rivers and floods, the difference in the height of areas (Zahak and Zabol are higher and Hirmand, Nimroz and Hamon are lower in height situation), the elevation, level of the water table (especially in the past years when a lot of floodwater entered the plain from the Hirmand River) are the most important factors that determine the salinity situation. However, on a farm scale, management of cultivation, fallow, leaching at the beginning of the season, irrigation, and removing of saline surface soils are decisive. Among them, agricultural activities on a smaller scale play an important role. despite the high variability of soil salinity at the field scale in the region, a relative general distribution is prevailed. The results of the study show more salinity in Nimroz and Hamon and less salinity in areas like Zahak and Zabol. The validation results of remote sensing studies showed that this technique can provide a suitable estimate of soil salinity in the Sistan plain and is a good quality method for monitoring of soil salinity changes.
Saeed Saadat: Sampling, Conceptualization, Validation, Supervision, Writing manuscript; Leila Esmaeelnejad: Conceptualization, methodology, Software, Manuscript editing; Hamed Rezaei: Sampling, consulting; Rasoul Mirkhani: Sampling
We have no permission to release data and codes.
We would like to express our sincere gratitude to the Research and Education Center for Agriculture and Natural Resources of Sistan and Baluchistan (Zabol) and Water and Soil Deputy, ministry of Jihad-e- Agriculture for the financial and logistics supports who significantly contributed during the research project.
The study was approved by the Ethics Committee of the Soil and Water Research Institute. The authors avoided data fabrication, falsification, plagiarism, and misconduct.
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